Regulations require aircraft brakes to be able to handle an aborted takeoff at any moment prior to the plane leaving the runway. Brakes should not exceed a specified temperature, to avoid performance degradation, so the regulations prohibit an aircraft from taking off if its brakes are too hot (e.g. above 400° C.). To ensure that the brakes are cool enough even after use during taxiing out to the runway, it is recommended that an aircraft is not dispatched if its brakes are above a predefined temperature (e.g. 150° C., as measured by a brake temperature sensor), which is significantly lower than the maximum permitted take-off temperature and allows for temperature increase during taxi braking.
Currently, the temperature of each brake pack on an aircraft is monitored using thermocouples placed in the brake pack which provide temperature measurements to a brake temperature monitoring system (BTMS) comprised in the avionics systems of the aircraft. The BTMS provides temperature information based on the measured temperature of each brake pack on the aircraft to the flight crew, to enable them to determine whether or not the brakes are cool enough to permit the aircraft to take off.
When all of the brake temperature sensors (i.e. the thermocouples) on an aircraft are functional, it is therefore not necessary to calculate a brake cooling time. However; for some aircraft a protocol (MMEL) exists which covers situations in which one or more brake temperature sensors are not functional (as well as other BTMS partial failure scenarios), and which may allow the aircraft to take off despite the non-functional temperature sensor(s) (or other partial failures).
For some cases the MMEL specifies that one when or more brake temperature sensors are non-functional, manual temperature measurements should be obtained for all brakes on the landing gear having the non-functional sensor(s). Manual temperature measurements must be taken from outside the brake pack, and so do not represent the same quantity as the measurements obtained by the BTMS sensors in the brake packs, but they can be used to qualitatively compare the temperature of different brakes on an aircraft.
If the manual temperature measurements for all of the brake packs having non-functional sensors are less than the manual temperature measurements for the hottest brake having a functional temperature sensor, then the MMEL permits a take-off determination to be made based only on the functional temperature sensors, and does not require a cooling time to be calculated. In all other cases (and in cases where manual temperature measurements are not obtained), the MMEL requires a brake cooling time to be calculated and applied, according to rules provided in the MMEL. The MMEL cooling time calculation rules are conservative to ensure that all brakes (including those with unknown temperatures, which may be hotter than the other brakes) have cooled to below 150° C. before aircraft dispatch. As a result of the conservativeness built into the MMEL cooling time calculation rules, an aircraft with a non-functional brake temperature sensor may wait significantly longer before being permitted to take-off than would have been the case if all of its brake temperature sensors had been functional.
US 2006/0241819 describes a method to compute brake cooling times by obtaining brake temperature measurements at two points in time (as determined using a timer), calculating a rate of cooling based on the measurements, and comparing the calculated rate to a stored temperature profile for brake cooling at an appropriate ambient temperature. A crude estimate of cooling time is determined based on this comparison. However; the method of US 2006/0241819 requires a functional brake temperature sensor and therefore cannot be used as an alternative to the MMEL calculation rules in situations where one or more brake temperature sensors of an aircraft are non-functional.
An improved system for predicting a brake cooling time is therefore desired.